Tuning unit



Jan. 5, 1937. J. P. PUTNAM ,0 9

TUNING UNIT Filed July 5, 1955 s Sheets-Sheet 1 -1 Fig.2. l

J. P. PUTNAM Jan. 5, 1937.

TUNING UNIT Filed July 5, 1955 3 Sheets-Sheet 2 J. P. PUTNAM Jan. 5, 1937.

TUNING UNIT Filed July 5, 1955 3 sheets sheet 3 Patented Jan. 5, 1937 UNITED STATES PATENT OFFICE TUNING UNIT Application July 5, 1935, Serial No. 29,866

14 Claims. (01. 250-40) This invention relates to tuning units for electric circuits and is especially adapted, although not limited, to radio receivers of the so-called all-wave type.

In receivers having a large frequency coverage it has heretofore been found necessary to employ a relatively large number of tuning elements in each tuning unit or stage and to use? an exceedingly complex circuit changing device having a very large number of contact members for switching from one set of tuning elements to another when passing from one frequency band to another.

It is therefore one of the objects of the present invention to provide a tuning unit for a radio receiver whereby a wide frequency range may be covered by a minimum number of tuning elements and such elements selected by an extremely simple circuit-changing device having a minimum number of contact members.

Each tuning unit or stage is self-contained and comprises two variable inductors, preferably in non-inductive relation, and a variable capacitor, together with circuit-changing means for connecting said capacitor in circuit with either inductor at will and means for smoothly and simultaneously varying the capacity of the capacitor and the inductances of the inductors.

The relation between the inductances of said inductors, which preferably are variometers disposed in non-inductive position, and the capacity of said capacitor depends upon the type of re ceiver in which the tuning unit is to be used; but whatever the type of receiver, the two inductors must have unequal maximum inductance.

In a superheterodyne receiver, the product of the minimum capacity of said capacitor by the minimum inductance of the inductor having the larger maximum inductance, preferably is greate1 than the product of the maximum capacity of said capacitor by the maximum inductance of the other of said inductors. In such case, the minimum inductance of one inductor preferably is higher than the maximum inductance of the other, and where variometers are employed as inductors this relation conveniently may be attained without unduly increasing the physical bulk of the unit by connecting the windings of one variometer in parallel and those of the other in series, and providing the variometer, the coils of which are serially connected, with a core comprising finely divided paramagnetic material and a binder.

Expressed in terms of frequency, the electromagnetic constants of the tuning unit, when used in a superheterodyne receiver, are such that the maximum frequency of the circuit formed by the capacitor and the inductor having the larger maximum inductance is less than the minimum frequency of the circuit formed by said capacitor and the other inductor.

When the tuning unit is used in a tuned radio frequency receiver, for example, the electromagnetic constants of said unit are such that the maximum frequency oi the circuit formed by the capacitor and the inductor having the larger maximum inductance preferably is equal to the minimum frequency of the circuit formed by the capacitor and the other inductor, but I do not wish to be understood as excluding the relation of said constants whereby the frequency of the first named circuit is slightly lower or slightly higher than that of the other.

Another object of my invention is to provide a convenient means for disposing the variometers in noninductive relation, such means comprising a rotary support of insulating material mounted for rotation in the! tuning-unit frame and formed of an integral structure having two coil-receiving cavities and two complementary coil-support members detachably secured thereto.

A further object is to provide means for spacing the plates of the condenser and insulating the same from each other at one point, and spacing and electrically connecting the same at another point, thereby to eliminate the formation of the closed circuits in the field of the variometer that would result from conductively connecting said plates at both spacing points.

Still another object is to provide means for eliminating the noises produced by electrical disturbances due to the relative movement of two contacting conducting members only one of which is grounded, this object being effected by mounting the rotor support member for rotation in openings formed in the metallic walls of the tuning-unit frame by means of insulating discs.

Various other objects and advantages of my invention, which is an improvement onthe tuning unit disclosed in my application, Serial No. 745,097 filed September 22, 1934, will appear in the detailed description of an embodiment of said invention which has given good results in practice and is illustrated in the accompanying drawings, in Which- Figure 1 is a plan View of a tuning unit embodying my invention.

Fig. 2 is a vertical section taken on the line 2-2 of Fig. l.

Fig. 3 is a vertical section taken on the line 3-3 of Fig. 1.

Fig. 4 is a vertical section taken on the line 44 of Fig. 1.

Fig. 5 is an end view showing the variometer rotor at a position 189 from that of Fig. 1, the condenser being omitted for the sake of clearness.

Fig. 6 is a vertical section taken on the line 6-6 of Fig. 1, the variometer and condenser ro-- tors being at a position 180 from that oi Fig. i.

Fig. 7 is a fragmentary section taken on the line 1--1 of Fig. 1.

Fig. 8 is a perspective view of one portion oi" the variometer rotors and the support member therefor.

Figs. 9 and 10 are perspective views of the other portions of said variometer rotors and the support members therefor.

Figs. 11 and 12 are perspective views of the variometer stators designed to co-operate with the rotors.

Fig. 13 is a diagram illustrating one type of circuit in which my tuning element may be employed.

In the particular drawings selected for more fully disclosing the principle of my invention, such drawings being illustrative merely and not restrictive, 20, 20 are parallel metallic plates held in spaced position by the studs 2! interposed between the same and secured at one end to one of said plates by screws 22, and at the other by the nuts 23 threaded to the reduced end portion 24 of said studs.

Enclosed within the frame formed by said plates and studs is the self-contained tuning unit comprising the two variable inductors, the common variable capacitor, and the circuit changing means above mentioned. When several units are to be connected in tandem, the threaded ends 24 of the studs of one unit threaded into the tapped holes in the studs of the next adjacent unit, into which tapped holes the screws 22 are threaded in the case of a single unit.

Referring to Figs. 8 to 12 inclusive, 35) is the frame or support member for the variometer rotors, such member preferably being an integral structure and comprising two portions arranged at right angles to each other. The portion 3| is provided with a spherical interior surface 32 in which the winding 33 is mounted. The complementary portion 34 also is provided with a spherical interior surface 35 in which is disposed the winding 36. The outer faces of the support members 3|, 34 are provided with registering circular apertures as indicated at 31. The stator windings 38 which co-operate with the rotor windings 33, 36 are mounted on the stator support 39 which has a spherical exterior surface. By means of the gudgeons Ml, which are received in the bearings formed by the complementary grooves M, M, formed in the members 3|, 34, respectively, the stator support is disposed in the proper position with respect to the rotor support, and is held in such position when said members are secured together by screws which pass through the registering holes M in said members.

The rotor support member is arranged in a plane at right angles to that of the member 3| and also has a spherical interior surface in which is mounted the winding 5!, the comple mentary rotor support member 5l, which has a spherical interior surface, carrying the winding 58. The stator support 52 has a spherical exterior surface on Which are mounted the windings 53 and is provided with gudgeons 54 whereby said stator is properly positioned within its cooperating rotor, said gudgeons being received in the bearings formed by the complementary grooves 55, 56, of the members 551, 51, respectively, and said members being secured together by screws 63 which pass through the registering holes 4 in said members. The pin E50 rigidly secured to one of the gudgeons 4i), and the pins 6!, [32? rigidly secured to the gudgeons 54, pass through and are held by the insulating bar 63 (Fig. l) secured to the frame members 28, said pins not only serving to hold the stator supports stationary, but also to afford terminals for connesting the variometer windings in circuit.

The stator windings 38 and the rotor windings 33, 36, are in the present instance connected in series and the stator windings 53 and the rotor windings SI, 53, preferably are connected in parallel, as indicated in Fig. 13.

Enclosed within the central bore 01 the stator support 39 and held in position by the bushing 6A is a core 65 of paramagnetic material preferably formed by mixing finely divided iron with a binder and compressing the same into the desired shape under extremely high pressure, such cores being well known articles of commerce and requiring no further description.

The variemeter rotor support is mounted for rotation in and between the tuning-unit frame by two insulating discs arranged respectively in oppositely disposed circular openings in the plates 20. One of said discs, 8%, is shown in the present instance as formed of two semicircular portions integral respectively with the parts ill and 34 of the rotor frame, and the other, ii'i, is secured by screws 68 to the flange E9 which is integral with said frame, said screws passing through the holes 15.

Preferably an antifriction ball H is interposed between the disc El and the plate spring 12 secured to one of the plates 2i]. In the particular embodiment of the invention shown in the drawings, the disc 66 has its bearing in the ballcage 73 which projects into one of the two oppositely disposed circular openings aforesaid in the plates 20, 20, the flange 14 on said cage holding the same in position. The metal disc 75 secured by screws, one of which is shown at T6, to the twopart insulating disc 66, carries the ball cup ll which projects into a cavity formed in the'wall of the ball-cage and with the periphery thereof forms a raceway for the antifriction balls "18. The dial knob H2 is suitably secured to the stud 7-5 integral with said disc '15, which is of smaller diameter than the interior diameter of the ball cage and does not make rubbing contact therewith.

By mounting the variometer rotor frame for rotation between the plates 20 by means of insulating discs, I eliminate the grinding noises that would be produced by the receiver if said discs were metallic, such noises being caused by electrical disturbances due to the relative movement of two contacting conducting members, only one of which is grounded.

By arranging the variometers at right angles to each other, inductive eirects between the two are eliminated, and by providing one of said variometers with a core having greater permeability than air, the magnetic field is concentrated and leakage reduced, thus insuring a greater flux linkage between the coils.

Another result obtained by using a magnetic core is that the figure of merit of the variometer, that is, the ratio of the total inductive reactance thereof to its total resistance, known as the Q of the variometer, is increased over the greater part of the variometer inductancerange or the ratio of its maximum to its minimum inductance. I have ascertained that the use of such core in a variometer is practically without effect on the Q thereof at and near the lower end of its inductive range where the coils are in or near the position of maximum opposition and minimum inductance.

The minimum inductance of a variometer is equal to the sum of the self inductances of the rotor and stator coils minus twice the mutual inductance thereof. As the rotor is turned toward the position of maximum assistance and maximum inductance, such maximum inductance being equal to the sum of the self inductances of the rotor and stator coils plus twice the mutual inductance thereof, the Q of the variometer is progressively increased and is a maximum at the upper end of the inductance range. It follows therefore that the use of said core results in a marked increase in the variometer inductance range, i. e., the ratio of the maximum inductance of the variometer to the minimum inductance thereof.

In the tuning unit herein particularly described the inductance range of each of the. variometers V, V', (Fig. 13) is approximately 10 1, as hereinafter more fully set forth, such ratio being specified herein merely by way of example and not as a limitation; and such relatively high inductance range is an important factor in the elimination of the relatively large number of tuning elements heretofore found necessary to be used in each tuning unit and the complex multi-contact switching member required for selecting the same when passing from one band to another.

The condenser rotor plates from each of which a portion has been cut to provide a trough 80, extending at right angles to the plane of each plate to accommodate the lower portion of the variometer rotor support, are secured to said rotor support by the bolts 83, 84 which pass through openings in said plates and the holes 85, 86, respectively, in the flanges 69, 69 formed integral with the variometer support member 30.

The variometer rotor and stator windings are connected to each other and to their respective: circuits by spiral hair-springs 81, 88, and 89, disposed in the semicircular slots 81, 38, and 89', respectively, formed in the rotor support 30. One end of each of said springs is connected electrically and mechanically to one of the stator gudgeons, and the other to a pin such as indicated at 90 (Fig. 2) in the body of the variometer rotor support.

The condenser stator plates 9I, from each of which is cut out a semicircular portion forming a trough 9| for accommodating the lower portion of the variometer rotor, are supported by the rails 92 spaced inwardly from the plates 20 and held in position by the screws 93. Screws 94, 95, pass through the registering apertures near the bottom of the plates BI and are suitably secured in the rails 92 for supporting said plates.

Means are provided for spacing each set of condenser plates in such manner that they will not form closed circuits acting as transformer secondaries in the field of the variometers, thereby absorbing and wasting energy. While this result may be eiTected by a variety of means, I prefer to employ for this purpose a plurality of flanged sleeves 96 (Fig. 7) of insulating material, one for each plate, each sleeve being disposed in the hole in one of the plates and the flange 96' thereof being interposed between a pair of adjacent plates and serving as a spacer. The bolts 83, 84, (in the case of the rotor condenser) pass through the central apertures of the said flanged sleeves. The outer ends of the condenser rotor plates 00 are spaced and electrically connected by the metallic washers 91.

In the case of the condenser stator, the insulating flanged spacers 96 are carried by the bolt 90 and metallic spacers 99 are carried by the bolt 95, the insulating spacers in each instance separating the plates at one point and insulating each from the other, and the conducting spacers separating and electrically connecting said plates at another point. In this way the formation of closed loops within the field of the variometers is eliminated.

Passing through the tuning unit frame is an insulating rod I0! on which is disposed an arcuate commutator member I02 the central portion of which is always in contact with the central brush I03 and the end portions of which make contact with the brush I94, or the brush I05, according to the angular position thereof. The brush members I03, I04, I05, may, as shown, conveniently be carried by the insulating bar 03, the ends of which are attached to the plates 20, 20.

In the position shown in Fig. 1, there is a metallic connection between the brushes I03, I04, as indicated diagrammatically in Fig. 13, and thereby the high frequency variometer V is con nected in circuit with the condenser C. By rotating the rod IOI about 90 degrees, a connecbetween the brushes I03, I05, is effected whereby the low frequency variometer V is connected in circuit with said condenser C.

Trimmer condensers I05, I01, preferably are employed as indicated in Fig. 13. By the term capacitor as used herein, it is to be understood that I include both the condenser C and the! particular trimmer condensers I06 or I01, electrically connected thereto by the circuit changing devices I02, I03, I04, and I05, if such trimmers are used. As shown in Fig. 13, the capacitor C and the inductor V or V connected thereto constitute a closed resonance circuit connected to the input or output side of the thermionic tube T or T.

The operation is as follows:

When the brush I03 is connected with brush I05 through the commutator I02 and the dial is at zero position, the circuit including the variometer V and condenser C will be attuned to its lowest frequency, approximately 220 kc, and as the dial is rotated counterclockwise from its zero position, the frequency of said circuit will be varied, without discontinuity, to about 2000 kc at which position the inductance of the low frequency variometer V and the capacity of said condenser are both at their minimum values. Within this frequency coverage are the aircraft radio beacon, maritime code and American broadcast bands, and a portion of the amateur bands. For higher frequency bands, the knob III is rotated clockwise about 90, thereby connecting the brushes I03, I04 through the commutator member I02 and put ting the high frequency variometer V in circuit with the condenser C. The dial is then brought to zero position, and then turned clockwise to vary the frequency of said circuit between approximately 2600 kc and 27,000 kc, within which frequency coverage is located practically the entire short-wave spectrum, including the police bands, the band allotted for communication from airplanes to ground, the international short-wave broadcast bands, and the greater portion of the amateur bands. It will be understood of course that the frequency values above specified are included herein. merely by way of example to facilitate the complete disclosure of one practical embodiment of my invention and that said invention is not limited thereto or to any particular frequency coverage.

When the tuning dial is at its 180 position, the inductance of the low frequency variometer V, which is then at its minimum value, is greater than the inductance of the high frequency variometer V when the dial is at its Zero posi-- tion, said high frequency variometer having its maximum inductance at such position. The condenser C being common to both variometers it follows that when the tuning unit is used in a superheterodyne receiver the maximum frequency of the circuit formed by the capacitor, i. e., the condenser C and the trimmer I06, if used, and the low frequency variometer V, preferably must not exceed the minimum frequency of the circuit formed by said capacitor, i. e., said condenser C and the trimmer I01, if used, and the high, frequency variometer V.

When the tuning unit is used in a tuned radio frequency receiver the maximum frequency of the circuit formed by the capacitor, i. e., the condenser C and the trimmer I06, if used, and the variometer V preferably is equal to the minimum frequency of the circuit formed by the capacitor, i. e., said condenser and the trimmer I01, if used, and the high frequency variometer V, although it may differ slightly therefrom,- in other words, there may be a small gap between the maximum frequency of one circuit and the minimum of the other, or else a small overlap of the same without substantial disadvantage.

When trimmer condensers such as I05, I01, are used, the tuning unit adapted for use in a superheterodyne receiver and in which there is a substantial gap between the maximum frequency of one circuit and the minimum of the other, may be converted into a tuning unit adapted for use in a tuned radio frequency receiver and in which the maximum frequency of one circuit is substantially equal to the minimum frequency of the other, by merely adjusting said trimmer condensers to seciu'e the substantial equality of said frequencies; but, if no trimmer condensers are employed, the maximum. inductance of the high frequency variometer V must be made larger to reduce the minimum frequency of its circuit to substantial equality with the maximum frequency of the circuit of the low frequency variometer V, if said variometer V remains unchanged, or else the minimum inductance of the low frequency variometer must be made smaller to increase the maximum frequency of its circuit to substantial equality with the minimum frequency of the high frequency variometer V, if said variometer V remains unchanged.

Preferably a metallic disc I08 of greater diameter than the insulating disc 61, is interposed between the latter and the flange 69 of the variometer rotor support, being" secured to the latter by the screws 68. The function of said disc I08 is to shield the tuning unit from electrical forces that would otherwise pass through the circular opening in the plate 20 within which the disc 51 is disposed. The disc m0, is insulated from the adjacent conducting elements by discs I09 of celluloid or other suitable non-conducting material. The opposite opening in the other plate is shielded by the ball-cage 2'3.

My improved tuning unit permits the covering of the entire range of frequencies used in radio communication by means of two ind ictors and a common capacitor connected in circuit with either inductor at will by switch having three contact members only in contradistinction to the tuning units now in use which require four or five inductors and a common capacitor interconnected at will by circuit-changing means having eighteen or more contact members.

By means of my invention, not only is the construction of a radio receiver greatly simplified and the cost thereof materially lessened, but also the weight and physical bull: of the apparatus is reduced. to a minimum.

Having thus disclosed an illustrative embodiment of my invention without however limiting the same thereto, what I claim and desire to secure by Letters Patent is:

1. A tuning unit comprising in combination, two variable inductors. of unequal maximum inductance, a variable capacitor, circuit changing means for connecting said capacitor in closed circuit with either of said inductors at will, and means connecting the capacitor and the inductors for simultaneous variation of the capacity of said capacitor and the inductances of said inductors.

2. A tuning unit comprising in combination, two variable inductors of unequal maximum inductance, the minimum inductance of one of said inductors being greater than the maximum inductance of the other, a variable capacitor, circuit changing means for connecting said capacitor in closed circuit with either of said inductors at will, and means connecting the capacitor and the inductors for simultaneous variation of the capacity of said capacitor and the inductances of said inductors.

3. A tuning unit comprising in combination, two variable inductors of unequal maximum inductance, a variable capacitor, circuit changing means for connecting said capacitor in closed circuit with either of said inductors at will, and means connecting the capacitor and the inductors for simultaneous variation of the capacity of said capacitor and the induetances of said inductors, the product of the minimum capacity of said capacitor by the minimum inductance of the inductor having the larger maximum inductance being greater than the product of the maximum capacity of said capacitor by the maximum inductance of the other of said inductors.

l. A tuning unit comprising in combination, two variable inductors of unequal maximum inductance, a variable capacitor, circuit changing means for connecting said capacitor in closed circuit with either of said inductors at will, and means connecting the capacitor and the inductors for simultaneous variation of the capacity of said capacitor and the inductances of said inductors, the maximum frequency of the circuit formed by said capacitor and one of said inductors being equal to the minimum frequency 7 of the circuit formed by said capacitor and the other of said inductors.

5. A tuning unit comprising in combination, two variable inductors of unequal maximum inductance, a variable capacitor, circuit changing means for connecting said capacitor in closed circuit with either of said inductors at will, and means connecting the capacitor and the inductors for simultaneous variation of the capacity of said capacitor and the inductances of said inductors, the maximum frequency of the circuit formed by said capacitor and the inductor having the larger maximum inductance being greater than the minimum frequency of the circuit formed by said capacitor and the other of said inductors.

6. A tuning' unit comprising in combination, two variable inductors of unequal maximum inductance, a capacitor, circuit changing means for connecting said capacitor in closed circuit with either of said inductors at will, and means connecting the capacitor and the inductors for simultaneous variation of the capacity of said capacitor and the inductances of said inductors, the maximum frequency of the circuit formed by said capacitor and the inductor having the larger maximum inductance not exceeding the minimum frequency of the circuit formed by said capacitor and the other of said inductances.

'7. A tuning device comprising in combination, two variometers of unequal maximum inductance, a variable capacitor, switch means for connecting said capacitor in closed circuit with either variometer at will, and means connecting the capacitor and the variometers for simultaneous variation of the capacity of said capacitor and the inductances of said variometers.

8. A tuning device comprising in combination, two variometers of unequal maximum inductance, said variometers being disposed in noninductive relation, a variable capacitor, switch means for connecting said capacitor in closed circuit with either variometer at will, and means connecting the capacitor and the variometers for simultaneous variation of the capacity of said capacitor and the inductances of said variometers.

9. A tuning device comprising in combination, two variometers of unequal maximum inductance, the minimum inductance of one of said variometers being greater than the maximum inductance of the other, a variable capacitor, switch means for connecting said capacitor in closed circuit with either variometer at will, and means connecting the capacitor and the va riometers for simultaneous variation of the capacity of said capacitor and the inductances of said variometers.

10. A tuning device comprising in combination, two variometers, one having its windings connected in parallel and the other having its windings connected in series, a variable capacitor, switch means for connecting said capacitor in closed circuit with either variometer at will and means connecting the capacitor and the variometers for simultaneous variation of the capacity of said capacitor and the inductances of said variometers.

11. A tuning device comprising in combination, two variometers, one having its windings connected in parallel and the other having its windings connected in series, a core of paramagnetic material for the variometer the windings of which are connected in series, a variable capacitor, switch means for connecting said capacitor in closed circuit with either variometer at will, and means connecting the capacitor and the variometers for simultaneous variation of the capacity of said capacitor and the inductances of said variometers.

12. A tuning unit comprising in combination, two variable inductors of unequal maximum inductance, a variable capacitor, circuit changing means for connecting said capacitor in circuit with either of said inductors at will, said capacitor and the inductor connected thereto constituting a closed resonance circuit, and means connecting the capacitor and the inductors for simultaneous variation of the capacity of said capacitor and the inductances of said inductors.

13. A tuning unit comprising in combination, two variable inductors of unequal maximum inductance, a variable capacitor, circuit changing means for connecting said capacitor with either of said inductors to form a closed resonance circuit, and means connecting the capacitor and the inductors for simultaneous variation of the capacity of said capacitcrand the inductances of said inductors.

14. A tuning unit comprising in combination, two variable inductors of unequal maximum inductance, a variable capacitor, circuit changing means for connecting said capacitor in circuit with either of said inductors at will, said capacitor and the inductor connected thereto constituting a closed resonance circuit, a thermionic tube, means connecting said resonance circuit to said tube, and means connecting the capacitor and the inductors for simultaneous variation oi the capacity of said capacitor and the inductances of said inductors.

JOHN P. PUTNAM. 

